1. Field of the Invention
The present invention relates to a high-damping elastomer composition suitable for vibration absorbing materials, shock absorbing materials and the like and, more particularly, to a high-damping elastomer composition suitable for use in vibration damping and vibration isolating applications in the architectural field.
2. Description of the Art
In the architectural field, vibration dampers and vibration isolators are used for suppressing vibrations of buildings which may be caused by earthquakes, winds, heavy motor vehicles in traffic, and the like. Therefore, damping materials for use in such vibration dampers and vibration isolators are required to have a capability of absorbing small- to large-amplitude vibrations in accordance with the rigidity of a building. In order to ensure a stable damping effect in the architectural field, the damping materials are further required to have stable damping characteristics in an open air environment around the building, and desirably have less temperature-dependent damping characteristics and rigidity in the temperature range between 0xc2x0 C. and 40xc2x0 C. Typically employed as the damping materials for use in such applications is a rubber composition comprising a rubber as a main component, and a polymer having a higher glass transition temperature (Tg), a resin having a lower softening temperature, or a filler such as carbon black, calcium carbonate or mica.
However, the rigidity of the conventional rubber composition becomes more temperature-dependent, if an attempt is made to improve the damping characteristics thereof. More specifically, the rubber composition has a higher hardness and hence an excessively high rigidity at a low temperature, and has a lower hardness and hence an excessively low rigidity at a high temperature. Therefore, the rubber composition is disadvantageous in that the rigidity thereof is highly temperature-dependent.
In view of the foregoing, it is an object of the present invention to provide a high-damping elastomer composition which provides a high damping effect and has less temperature-dependent damping characteristics and rigidity.
To achieve the aforesaid object, the high-damping elastomer composition according to the present invention comprises:
(A) a styrene-isoprene-styrene triblock copolymer; and
(B) an ethylene-methyl methacrylate random copolymer.
A conventional approach to the improvement of the damping characteristics is to utilize the structural change of a matrix material at the glass transition temperature thereof. More specifically, the matrix material is designed so that the glass transition temperature thereof falls within a predetermined temperature range in which the damping material is required to provide the damping effect. Although this approach ensures a high damping effect, there are great variations in mechanical characteristics, such as damping characteristics and rigidity, of the damping material depending on the temperature because this approach utilizes the structural change of the matrix material from the glassy state to the rubbery state in the predetermined temperature range. As a result of intensive studies, the inventors of the present invention have come up with an idea of providing a major damping effect by utilizing interactions in interfaces between matrix domains in a partially compatibilized blend while providing a temperature-dependent damping effect only in the predetermined temperature range by utilizing the structural change of the matrix material at the glass transition temperature. The inventors have further conducted research and development on the partially compatibilized system, and finally found that a styrene-isoprene-styrene triblock copolymer (component A) and an ethylene-methyl methacrylate random copolymer (component B) can be blended in a partially compatibilized state, thereby achieving the aforesaid object. Thus, the inventors have attained the present invention. More specifically, the styrene-isoprene-styrene triblock copolymer (component A) and the ethylene-methyl methacrylate random copolymer (component B) form a so-called xe2x80x9cislands-in-the-seaxe2x80x9d structure, which may vary depending on the blending ratio between the components A and B, in the inventive high-damping elastomer composition, and are partially compatibilized with each other in a homogeneously mixed state in sea-island interfaces. When a force is externally applied to the composition in a certain cycle, homogenization and segregation of the components A and B occur in the sea-island interfaces (in a macroscopic sense, assimilation and dissimilation of the components A and B occur in the see-island interfaces). At this time, the elastomer composition consumes the energy of the force, thereby providing a high damping effect. The elastomer composition, which is a partially compatibilized system, is free from substantial phase transition and, hence, has less temperature-dependent damping characteristics.
Where the blending ratio between the styrene-isoprene-styrene triblock copolymer (component A) and the ethylene-methyl methacrylate random copolymer (component B) is set to fall within a particular range, the partial compatibilization of the components A and B is promoted to further improve the damping characteristics of the elastomer composition.
Where the elastomer composition contains a tackifier in addition to the styrene-isoprene-styrene triblock copolymer (component A) and the ethylene-methyl methacrylate random copolymer (component B), the tackifier functions as an interphase controlling agent for partially compatibilizing the components A and B with each other, so that the partial compatibilization of the components A and B is further facilitated.
Where the elastomer composition contains a plasticizer in addition to the styrene-isoprene-styrene triblock copolymer (component A) and the ethylene-methyl methacrylate random copolymer (component B), the glass transition temperature (Tg) can be controlled as desired, so that the hardness and the temperature dependence of the elastomer composition can more easily be controlled.